Cooling systems for rotary engines

ABSTRACT

Cooling systems for rotary internal combustion engines. Air through-rotor cooling is provided by a closed-loop cooling system with an output shaft-driven fan. Liquid cooling is provided utilizing a cooling chamber within the output shaft.

CROSS REFERENCE TO RELATED APPLICATION

This application is a non-provisional application claiming priority fromUK Application No. 1220888.0 filed on Nov. 21, 2012, incorporated hereinby reference in its entirety.

FIELD OF THE DISCLOSURE

The present description relates generally to rotary engines and moreparticularly to cooling systems for rotary engines.

BACKGROUND OF RELATED ART

In a number of applications rotary internal combustion engines (forexample, the Wankel layout) provide an attractive alternative to themore commonly utilized reciprocating piston engine.

In a rotary engine a rotor is mounted eccentrically on an output shaft.The rotor is geared to the shaft such that rotation of the output shaftcauses eccentric rotation of the rotor, and vice versa. For example, aWankel engine uses a three-side (approximately triangular) rotor withinan epitrochoidal chamber.

Cooling of a rotary engine can present challenges. Reciprocating pistonengines are typically either air cooled through the crankcase, cylinderblock and heads, or water cooled by water flow paths in the cylinderblock. Oil supplied to the crank shaft also assists with cooling.Although a similar water cooling system can be implemented for a rotaryengine, cooling of the output shaft and gearing linking that shaft tothe rotor is inefficient as those components are far removed from thecooling medium.

Furthermore, the gears and bearings in the interior of the rotor must belubricated, which makes circulating cooling media in that areadifficult.

There is therefore a requirement for improved cooling systems for rotaryengines.

The embodiments described below are not limited to implementations thatsolve any or all of the disadvantages of known publish/subscribesystems.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

There is provided a rotary internal combustion engine, comprising aclosed-loop cooling system having a closed-loop fluid flow path throughthe interior of a rotor of the engine and a heat exchanger, and a fanconfigured to circulate a fluid around the flow path, wherein the fan ismounted on and driven directly by the engine's output shaft.

The fluid may be a gas.

The gas may be a gas which has blown-past the rotor's side-seals.

The fan may be a centrifugal fan.

The fan may have a diameter of 160 mm or greater.

The closed-loop cooling system may comprise a pressure-relief valveconfigure to limit the maximum pressure in the closed-loop fluid flowpath.

The closed-loop cooling system may comprise an oil injector forinjecting oil into gas flowing in the closed-loop fluid flow path forlubricating the interior of the rotor.

The closed-loop cooling system may comprise an oil injector forinjecting oil into gas flowing in the closed-loop fluid flow path forlubricating the interior of the rotor.

There is also provided a rotary internal combustion engine, comprisingan output shaft having an internal cooling chamber with a closed distalend within the output shaft, and an open proximal end at an end of theoutput shaft; a tube within the cooling chamber spaced from the internalwall of the cooling chamber and from the distal end of the coolingchamber, the tube and cooling chamber forming a cooling flow-paththrough the center of the tube, between the end of the tube and thedistal end of the cooling chamber, and between the exterior surface ofthe tube and the interior surface of the cooling chamber; and animpeller for circulating water through the cooling flow-path.

The tube may be stationary with respect to the engine body.

The impeller may be mounted on the open end of the output shaft.

The exterior surface of the tube may be spaced from the interior surfaceof the cooling chamber by 2 mm or more.

The preferred features may be combined as appropriate, as would beapparent to a skilled person, and may be combined with any of theaspects of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example, withreference to the following drawings, in which:

FIG. 1 shows a schematic block diagram of a cooling system;

FIGS. 2 and 3 show cross-sections through a rotary engine comprising anembodiment of a cooling system;

FIGS. 4 and 5 show cross-sections through a rotary engine comprising anembodiment of a cooling system; and

FIGS. 6 and 7 show cross-sections through a rotary engine comprising anembodiment of an output shaft cooling system.

Common reference numerals are used throughout the figures to indicatesimilar features.

DETAILED DESCRIPTION

Embodiments of the present invention are described below by way ofexample only. These examples represent the best ways of putting theinvention into practice that are currently known to the Applicantalthough they are not the only ways in which this could be achieved. Thedescription sets forth the functions of the example and the sequence ofsteps for constructing and operating the example. However, the same orequivalent functions and sequences may be accomplished by differentexamples.

FIG. 1 shows a schematic diagram of a cooling system for a rotaryengine. A closed cooling circuit is provided to circulate cooling fluidthrough the interior of the rotor 10 to remove heat from the engine. Thecooling circuit flows fluid comprises a fan 11 to drive cooling fluidaround the circuit. A heat exchanger 12 extracts heat from the coolingfluid, for example by heat exchange to atmospheric air in a gas-gas heatexchanger or to a coolant liquid in a gas-liquid heat exchanger.

The cooling fluid flows from the heat exchanger 12 back to the rotorinterior 10 to complete the closed circuit. The cooling circuit may bepressurized by gasses blowing past the rotor side seals and accordinglya pressure relief valve 13 may be provided to limit the pressure withinthe cooling circuit.

An oil injector 14 is provided to inject oil into the cooling fluid tolubricate the working parts in the interior of the rotor. Since thecooling circuit is a closed loop, the oil circulates continuously and isonly lost via leakage at the side seals of the rotor into the combustionchamber. The oil creates a film over the side plates which is then burntin the combustion process. Previous cooling systems have used a totalloss lubrication system which is both expensive to run andenvironmentally unfriendly. The closed-loop arrangement mitigates thesedisadvantages. In an embodiment the oil injector is a high-pressureinjector capable of injecting oil into the pressurized cooling systemwithout utilizing a pressurized reservoir. As explained above, thecooling system may be pressurized to 1 bar. A low-pressure injectorcould be utilized by also pressurizing the reservoir.

Where a non-pressurized oil reservoir is utilized the vent of thepressure release valve may be fluidly connected to the oil reservoirsuch that air exiting through the pressure release valve passes throughthe oil reservoir on its path to atmosphere. Oil suspended in thereleased cooling gasses is collected in the oil reservoir before thegasses are vented to atmosphere. This arrangement allows recycling ofthe oil, thereby reducing oil use.

FIG. 2 shows a cross-section through a rotary engine parallel with, andthrough, the output shaft 20. FIG. 3 shows a cross through A-A in FIG.2. With the exception of the points highlighted below the engine shownin FIGS. 2 and 3 is conventional and its operation will therefore beapparent to the person skilled in the art. The engine of FIGS. 2 and 3comprises a cooling system as described with reference to FIG. 1. In anexample engine, the combustion chamber volume is 300 cc.

The rotor 21 is provided with at least one opening 22 such that a flowpath is open from a first side to a second side of the rotor to allowthe flow of fluids through the rotor 21 parallel with the output shaft20. In an example, the at least one opening 22 may be semi-circular inshape with a 20 mm radius. Openings 23 are also defined in the first 25and second 26 side plates such that fluids can enter the interior of therotor 21, flow through the at least one opening 22 in the rotor 21, andexit through the other side plate. The side plate openings 23 arepositioned within the path traced by the rotor side seals duringrotation of the rotor 21 such that they do not disrupt the seal createdby those seals. This leads to the ‘lemon’ shape of opening seen in thefigures. In a typical example, the opening has dimensions of 95 mm and65 mm on the long and short axis.

A centrifugal fan 27 is mounted on the output shaft 20 such that it isdriven by and rotates with the output shaft 20. The opening 23 in thefirst side plate 26 forms a flow path from the rotor interior to thecenter, inlet, of the centrifugal fan 27. An annular outlet flow path 28is defined at the exterior of the fan 27 to collect the output from thefan 27. As will be appreciated, the flow path 28 is shown as acontinuous annulus in FIG. 3, but alternative shapes may be utilizedaccording to design requirements. The dimensions of the flow path 28increase in an axial direction around the flow path, but not in a radialdirection. This provides an increase in cross-sectional area of the flowpath 28, giving improved fan performance, without increasing thediameter of the fan housing.

The direct mounting of the fan 27 on the output shaft 20 removes arequirement for a geared or belt connection to drive the fan 27. Thisdirect connection has improved mechanical efficiency, thereby improvingengine power output. Due to the direct mounting of the fan 27 it rotatesat the same speed as the output shaft 20 and cannot be geared to providea higher speed and hence greater output. The limitation in fan speed,and associated reduction in output, has previously been thought toprevent direct mounting of the fan.

A fan capable of providing sufficient output when rotating at typicaloutput shaft speeds has now been designed, thereby allowing thismounting. In an example embodiment, a suitable fan may be centrifugalfan, 160 mm in diameter with forwarding curving blades of 10 mm height.In further embodiments the fan diameter may be larger than 160 mm. In anexample, the fan should be capable of providing an airflow with adynamic pressure of 12″ water gauge (48 kPa).

As well as improved mechanical efficiency, the direct mounting of thefan also provides a reduced physical size and simpler construction.

An outlet port 29 in the fan output flow path provides for a fluidconnection through a heat exchanger and back to the opening in thesecond side plate 25, thereby providing a closed flow path as describedwith reference to FIG. 1. The parts of the cooling circuit not shown inFIGS. 2 and 3 may be provided as exterior parts connected to the engine,or in alternative designs may be provided as part of the engine itself

As seen in FIG. 2 the rotor side seals 30 form part of the wall of theclosed cooling circuit. Gasses blowing past those seals 30 pressurizethe cooling circuit, thereby providing a pressurized cooling medium. Theincrease in pressure gives a denser cooling medium with an increasedheat capacity, thereby increasing the cooling ability of the circuit.The blow-past gasses are combustion gasses and are hence hot. However,since the system is a closed loop this initially higher temperature isreduced and the gasses then serve as coolant. Once the cooling circuitis pressurized the blow-past is minimal due to the approximately equalpressures either side of the side seals and therefore there is notcontinuous flow of hot gasses into the cooling circuit.

As noted above, a pressure relief valve is provided in the coolingcircuit to prevent the pressure increasing above a predetermined level,for example 1 bar which is bled off back into the oil reservoir andre-cycled into the closed cooling/lubrication circuit. The output shaftmain seals 31, 32 also form part of the cooling circuit wall and thispressure limitation protects those seals from damage.

In use, as the engine starts up the output shaft 20 drives the fan 27which circulates cooling fluid around the closed circuit. Blow past theside seals 30 increases the pressure in the cooling system. As thepressure in the cooling circuit increases blow-past reduces due to thereduced pressure difference between the combustion chambers and thecooling circuit. The fan circulates the gasses around the coolingcircuit. The temperature of the gasses reduces from the combustiontemperature due to heat transfer through the heat exchanger, and thegasses then transport heat from the rotor interior to the heatexchanger, thereby cooling the engine.

FIGS. 4 and 5 show an alternative configuration for implementing thecooling system of FIG. 1. Functionally the configuration is the same asdescribed hereinbefore, but the fan 40 is mounted in a separate housingto the main engine parts. The fan 40 is mounted on the output shaft 20as described above. The fan inlet and outlet 28 are connected to theside plate openings by fluid conduits exterior to the engine (notshown).

FIG. 6 shows a cross-section parallel with and through the output shaft60 of a rotary engine comprising a further embodiment of a coolingsystem. Apart from the features described below, the function andoperation of the engine shown in FIG. 6 is conventional. FIG. 7 shows across-section through line A-A in FIG. 6.

The output shaft 60 is at least partially hollow comprising alongitudinal cooling chamber 61 extending along the axis of the outputshaft 60 from a first end 62 to a second closed end 63.

A water impeller 64 is attached to the open end 62 of the output shaft60 to turn with that output shaft 60. A water pump housing 65 enclosesthe water impeller 64 and the open end 62 of the output shaft 60. Theoutput shaft 60 is sealed to the engine body by a seal 66 to create asealed chamber 67. In an example embodiment the water impeller is 50 mmin diameter. As will be appreciated, the diameter of the impeller may beselected according to the required circulation of the cooling system.

A tube 68 extends through the water pump housing 65 and into the coolingchamber 61 within the output shaft 60. The tube 68 is sized such that itis spaced from the interior of wall of the output shaft 60 to allowcooling fluid to flow between the tube 68 and the output shaft 60. Thatspace is in fluid communication with the inlet to the impeller 64. Thetube 68 is attached and sealed to the water pump housing 65 and soremains stationary with respect to the engine body, and does not rotatewith the output shaft 60.

In an example embodiment the inner diameter of the cooling chamber is 20mm. In further embodiments the diameter may be greater than 20 mm. In anexample, the inner diameter of the tube 68 is 13 mm and the outerdiameter is 15 mm. These dimensions, when used with a 20 mm diametercooling chamber, provided a flow path around the outside tube having aheight of 2.5 mm and extending around the circumference of the tube. Inalternative embodiments different dimensions may be utilized.

An inlet to the tube 68 is provided for connection to the output of theimpeller 64 via a heat exchanger to form a closed cooling path. Theclosed cooling path is typically filled with water to act as a coolingmedium, but as will be appreciated other coolant fluids may be utilized.

In use the impeller 64 is rotated by the output shaft 60 and pumps fluidaround the cooling circuit through the heat exchanger, into the centerof the tube 68, and back through the output shaft 60 to the impeller 64inlet.

The cooling circuit described in relation to FIG. 6 achieves directcooling of the output shaft 60 while only requiring a single additionalwater seal 66 compared to uncooled systems. The input and output of thewater flow path are on a single side of the engine reducing thedimensions required to add the cooling system. The interior of theoutput shaft 60 is in very close proximity (both physically andthermally) to the output shaft eccentric bearing and rotor gearingthereby providing efficient heat transfer from those components to thecooling fluid.

The cooling chamber is shown extending to approximately the center ofthe eccentric bearing, but as will be appreciated the length of thechamber may be selected to provide the required thermodynamicperformance.

Two cooling systems have been described hereinbefore for cooling rotaryengines. The two systems may be utilized alone or in combination.

As will be appreciated a more than one rotor, and associated chamber andcomponents, may be arranged along the length of the output shaft. Insuch engines suitable openings between the rotor interiors may beprovided to guide coolant flow through the rotors. Similarly, theopening in the output shaft may extend along an appropriate length toprovide cooling to the shaft in the region of more than one rotor.

Any range or device value given herein may be extended or alteredwithout losing the effect sought, as will be apparent to the skilledperson.

It will be understood that the benefits and advantages described abovemay relate to one embodiment or may relate to several embodiments. Theembodiments are not limited to those that solve any or all of the statedproblems or those that have any or all of the stated benefits andadvantages.

Any reference to ‘an’ item refers to one or more of those items. Theterm ‘comprising’ is used herein to mean including the method blocks orelements identified, but that such blocks or elements do not comprise anexclusive list and a method or apparatus may contain additional blocksor elements.

It will be understood that the above description of a preferredembodiment is given by way of example only and that variousmodifications may be made by those skilled in the art. Although variousembodiments have been described above with a certain degree ofparticularity, or with reference to one or more individual embodiments,those skilled in the art could make numerous alterations to thedisclosed embodiments without departing from the spirit or scope of thisinvention.

We claim:
 1. A rotary internal combustion engine, comprising aclosed-loop cooling system having a closed-loop fluid flow path throughthe interior of a rotor of the engine and a heat exchanger; and a fanconfigured to circulate a fluid around the flow path, wherein the fan ismounted on and driven directly by the engine's output shaft.
 2. Anengine according to claim 1, wherein the fluid is a gas.
 3. An engineaccording to claim 2, wherein the gas is gas which has blown-past therotor's side-seals.
 4. An engine according to claim 1, wherein the fanis a centrifugal fan.
 5. An engine according to claim 1, wherein the fanhas a diameter of 160 mm or greater.
 6. An engine according to claim 1,wherein the closed-loop cooling system comprises a pressure-relief valveconfigured to limit the maximum pressure in the closed-loop fluid flowpath.
 7. An engine according to claim 1, wherein the closed-loop coolingsystem comprises an oil injector for injecting oil into gas flowing inthe closed-loop fluid flow path for lubricating the interior of therotor.
 8. An engine according to claim 7 when dependent on claim 6,wherein a vent outlet of the pressure-relief valve is fluidly coupled toa reservoir of the oil injector.
 9. A rotary internal combustion engine,comprising an output shaft having an internal cooling chamber with aclosed distal end within the output shaft, and an open proximal end atan end of the output shaft; a tube within the cooling chamber spacedfrom the internal wall of the cooling chamber and from the distal end ofthe cooling chamber, the tube and cooling chamber forming a coolingflow-path through the centre of the tube, between the end of the tubeand the distal end of the cooling chamber, and between the exteriorsurface of the tube and the interior surface of the cooling chamber; andan impeller for circulating water through the cooling flow-path.
 10. Anengine according to claim 9, wherein the tube is stationary with respectto the engine body.
 11. An engine according to claim 9, wherein theimpeller is mounted on the open end of the output shaft.
 12. An engineaccording to any of claims 9 wherein the exterior surface of the tube isspaced from the interior surface of the cooling chamber by 2 mm or more.